This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-080850 filed on Mar. 22, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a vehicle braking control apparatus. More specifically, the present invention pertains to a braking control apparatus for vehicles which is able to generate a master cylinder pressure including a first fluid pressure in response to a pedal depression force and a second fluid pressure corresponding to a fluid pressure introduced by a pressure apply device and to control a braking force of each wheel in response to the pedal depression force or a vehicle condition.
A known vehicle braking control apparatus is disclosed in German Offenlegungsschrift No. DE 197 03 776 A1. In this apparatus, pressure responsive to the pedal depression force is detected by a pressure sensor and the pedal depression force is amplified by a hydraulic booster and transmitted to the piston of a master cylinder by moving a booster piston by the boosted fluid pressure. When used in vehicle stability control, the boosted fluid pressure is amplified in the hydraulic booster and transmitted to the piston of the master cylinder by introducing the boosted fluid pressure necessary for generating the desired brake fluid pressure to the booster chamber. Accordingly, during the turning of the vehicle, the vehicle stability control is operated by introducing the boosted fluid pressure in response to a vehicle condition. Vehicle stability control refers to the control of the braking force of each wheel in order to decrease the difference between a target running line for the vehicle and an actual running line of the vehicle based on the detected results of the vehicle condition (the amount of the vehicle condition) during steering while the vehicle is turning for instance.
In the known apparatus, brake fluid pressure in response to the pedal depression force is continuously supplied to the wheel brake cylinder of each wheel from the master cylinder. This is because a signal from the pressure sensor takes precedence over the vehicle stability control sensor. Accordingly the vehicle stability control is stopped even when vehicle stability control may still be necessary. That is, the control is stopped in spite of a vehicle condition in which vehicle stability control is still needed. The problem is that the stability of the vehicle is not assured during turning because the vehicle stability control for reducing understeer or oversteer is stopped by the depression of the brake pedal in the case of strong understeering or oversteering during the turning. In other words, the braking force which satisfies a deceleration demand to the non-controlled wheels cannot be generated while continuing the vehicle stability control when a driver needs to decrease the vehicle speed and thus depresses the brake pedal during vehicle stability control.
In light of the foregoing, a need exists for a braking control apparatus for vehicles that is capable of generating a braking force in response to a pedal depression force to the non-controlled wheels while still continuing the vehicle stability control.
In accordance with one aspect of the invention, a vehicle braking control apparatus includes a fluid pressure generator that generates a brake fluid pressure including a pedal input pressure component in response to a pedal depression force and a servo pressure component in response to fluid pressure introduced by a pressure apply device, a fluid supplying mechanism supplying the brake fluid to wheel cylinders of each wheel from a master cylinder, and a controller controlling the fluid pressure introduced by the pressure apply mechanism in response to a vehicle condition and controlling the braking force of each wheel by driving the fluid supplying mechanism in response to the pedal depression force or the vehicle condition. A pedal input pressure estimating device estimates the pedal input pressure, and the controller controls the braking force of the non-controlled wheels during vehicle stability control based on the pedal input pressure estimated by the pedal input pressure estimate device.
With the present invention, when the brake pedal is depressed during vehicle stability control, the pedal input pressure in response to the pedal depression force is estimated correctly and the braking force of the non-controlled wheels during vehicle stability control is controlled. As a result, the vehicle can be decelerated with a deceleration in response to the pedal depression force. That is, the deceleration does not give any undesirable feeling to the driver even during vehicle stability control.
The vehicle braking control apparatus also includes a fluid pressure sensor detecting the master cylinder pressure of the brake fluid pressure generated in the master cylinder. The pedal input pressure estimating device calculates the servo pressure based on a value of a control signal outputted from the controller to the pressure apply device, and estimates the pedal input pressure by subtracting the calculated value of the servo pressure from that of the master cylinder pressure. The pedal input pressure in response to the amplified pedal depression force is thus estimated correctly based on the value of the control signal outputted to the pressure apply device and the master cylinder pressure detected by the fluid sensor.
The pedal input pressure estimating device holds the estimated value of the pedal input pressure calculated previously when a pressure increase signal increasing the brake fluid pressure of any of the wheel cylinders of the wheels is outputted during vehicle stability control, and the controller controls the braking force of the non-controlled wheels based on the estimated value of the pedal input pressure held previously. Thus, when the pressure increase signal amplifying the brake fluid of any wheel cylinder during vehicle stability is outputted, the estimated value of the pedal input pressure calculated previously is assured. As a result, when the master cylinder pressure starts to decrease by the opening of a holding valve receiving the pressure increase signal and by a fluid amount consumption of the wheel cylinders while the pedal depression force is constant or increasing, a fault judgment in which the pedal input pressure is also decreased can be prevented.
The pedal input pressure estimating device holds the estimated value of the pedal input pressure when the master cylinder pressure detected by the fluid pressure sensor is turned to be increased while a predetermined period is passed from the ending of the outputting of the pressure increase signal, and estimates the value decreased by a predetermined value from the estimated value of the pedal input pressure held previously when the master cylinder pressure continues to decrease. Accordingly, when the master cylinder pressure begins to increase from a decreasing state within a predetermined time from the ending of the pressure increase outputting, the estimated value of the pedal input pressure calculated previously is assured. On the other hand, when the master cylinder pressure continues to decrease within the predetermined time, the pedal input pressure is decreased from the estimated value calculated previously because the pedal depression force is judged to be decreased. As a result, whether or not the brake pedal is still depressed is judged correctly after the pressure increase outputting, and the braking force of the non-controlled wheels can be generated correctly.
The pedal input pressure estimating device increases a pressure change correcting amount added to the estimated value of the pedal input pressure calculated previously when the pressure increase signal is outputted, and decreases the pressure change correcting amount after the ending of outputting of the pressure increase signal. Because the pressure change correcting amount increased or decreased in response to the pressure changing of the master cylinder pressure is added to the pedal input pressure calculated from the master cylinder pressure, the pedal depression force after the correcting can be estimated to the correct value which is not influenced by the pressure changing of the master cylinder pressure.